Infrared spectroscopy is one of the most diffused and powerful technique in the field of Heritage Science, thanks to its capability to identify different materials and their degradation products, also at the microscopic scale. In this thesis work, Fourier Transform Infrared spectroscopy (FTIR) has been exploited for the study of the degradation processes of the so-called “Cadmium yellows”, synthetic pigments based on Cadmium sulfide produced since the nineteenth century and used in oil paintings. Many are the problems encountered in renowned easel paintings and masterpieces, as those of Picasso, Matisse, Seurat, Van Gogh, Mirò and Ensor, in which this pigment was used: fading of the yellow colour, embrittlement, loss of adhesion, chalking, flaking and spalling, formation of dark or whitish surface layers. Understanding the reasons why these changes happen and in what conditions is of paramount importance for the conservation and restoration of such invaluable heritage. Mock-up samples simulating the painting layer were prepared starting from pigments obtained through different synthesis processes, with linseed oil as binding medium. The resulting samples were subjected to an accelerated ageing process under UV irradiation at room temperature and in controlled high relative humidity conditions. The samples were analyzed by FTIR spectroscopy in the mid-IR range, before and after ageing. Different FTIR sampling techniques (diamond crystal ATR; Ge crystal micro-ATR; micro-reflection; diamond cell micro-FTIR transmission) were used and compared to assess the changes that occurred in the painting layer. The attention has been focused on the potentiality of the different FTIR techniques for the study of the impact of the synthesis factors on the ageing and degradation of the different painting layers. In addition, the study of a micro-fragment coming from the deteriorated painting “Stadtende/Häuserbogen III” by Egon Schiele (Neue Galerie Graz, Universalmuseum Joanneum, Austria) has been carried out, and a first hypothesis about the degradation pathway was proposed.
La spettroscopia infrarossa è tra le tecniche di analisi più usata ed efficace nell’ambito dei beni culturali, grazie alla sua capacità di caratterizzare diversi materiali e i loro prodotti di degradazione, anche su scala micrometrica. In questo lavoro di tesi, la spettroscopia infrarossa a trasformata di Fourier (FTIR) è stata applicata allo studio dei processi di degradazione dei cosiddetti “gialli di Cadmio”, pigmenti sintetici a base di solfuro di Cadmio prodotti a partire dal diciannovesimo secolo, usati in dipinti a olio. Molti sono i problemi riscontrati in importanti e rinomati dipinti, come quelli di Picasso, Matisse, Seurat, Van Gogh, Mirò ed Ensor, nei quali questo pigmento è presente: scolorimento del colore giallo, infragilimento e conseguente perdita di adesione dello strato pittorico in alcuni punti, formazione di depositi scuri o bianchi sulla superficie del dipinto. Comprendere il motivo di questi cambiamenti e le condizioni in cui avvengono è di fondamentale importanza per il mantenimento e il restauro di beni artistici inestimabili. Campioni simulanti lo strato pittorico sono stati preparati utilizzando pigmenti sintetizzati con diversi metodi e olio di lino come legante. I campioni così ottenuti sono stati sottoposti ad un processo accelerato di invecchiamento con luce UV a temperatura ambiente e condizioni di umidità controllata. Diverse metodologie di spettroscopia FTIR sono state utilizzate e confrontate per l’analisi dei campioni (ATR con cristallo di diamante, micro-ATR con cristallo di Germanio, micro-riflessione e micro-trasmissione in cella di diamante), ponendo l’attenzione sulle potenzialità di questa tecnica per lo studio dei fattori che influenzano l’invecchiamento e il degradato dello strato pittorico. Inoltre, è stato condotto uno studio su un micro-frammento proveniente dal dipinto deteriorato “Stadtende/Häuserbogen III” di Egon Schiele, conservato nel museo Neue Galerie Graz, Universalmuseum Joanneum (Austria) ed è stata fatta una prima ipotesi sul meccanismo di degradazione.
Study of the degradation process of Cadmium Yellow pigments by means of Fourier Transform Infrared (FTIR) Spectroscopy
DA SOGHE, FLAVIA
2019/2020
Abstract
Infrared spectroscopy is one of the most diffused and powerful technique in the field of Heritage Science, thanks to its capability to identify different materials and their degradation products, also at the microscopic scale. In this thesis work, Fourier Transform Infrared spectroscopy (FTIR) has been exploited for the study of the degradation processes of the so-called “Cadmium yellows”, synthetic pigments based on Cadmium sulfide produced since the nineteenth century and used in oil paintings. Many are the problems encountered in renowned easel paintings and masterpieces, as those of Picasso, Matisse, Seurat, Van Gogh, Mirò and Ensor, in which this pigment was used: fading of the yellow colour, embrittlement, loss of adhesion, chalking, flaking and spalling, formation of dark or whitish surface layers. Understanding the reasons why these changes happen and in what conditions is of paramount importance for the conservation and restoration of such invaluable heritage. Mock-up samples simulating the painting layer were prepared starting from pigments obtained through different synthesis processes, with linseed oil as binding medium. The resulting samples were subjected to an accelerated ageing process under UV irradiation at room temperature and in controlled high relative humidity conditions. The samples were analyzed by FTIR spectroscopy in the mid-IR range, before and after ageing. Different FTIR sampling techniques (diamond crystal ATR; Ge crystal micro-ATR; micro-reflection; diamond cell micro-FTIR transmission) were used and compared to assess the changes that occurred in the painting layer. The attention has been focused on the potentiality of the different FTIR techniques for the study of the impact of the synthesis factors on the ageing and degradation of the different painting layers. In addition, the study of a micro-fragment coming from the deteriorated painting “Stadtende/Häuserbogen III” by Egon Schiele (Neue Galerie Graz, Universalmuseum Joanneum, Austria) has been carried out, and a first hypothesis about the degradation pathway was proposed.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/169274